Human gait is a symphony of systems who’s basic rhythm is conducted by the brain.
If you’re a forward thinking and educated trainer or therapist you most likely use gait during your assessment procedures and rightly so, as efficient gait represents balance between neurological function, biomechanics and the forces of gravity all expressed via an autonomous pattern. As such it offers the perfect platform for movement assessment.
To date the Health and Fitness Industry has become fairly comfortable with the mechanical model of upright locomotion; Ground reaction force; deceleration of joint motion via the eccentric loading model and theory of the kinetic chain.
As AMN was formed out of a fascination with the governing system of the body, the brain, we would like to present some of the magic behind the mechanics.
Knowledge has to be improved, challenged & increased constantly or it vanishes | Peter Drucker
When i first tried to usefully observe the intricacies of human gait, I literally just saw a person walking away from me and had more to say on their choice of shorts than how their body was loading.
Only when I was told what to look for did my gait glaucoma gradually begin to clear. A trained eye observing joint mechanics in motion can skilfully pick out where the system may be restricted. We can see what motions are lacking and if we have an effective exercise system we can intervene to try and give the elusive joint motions back to the client.
I reached a stage where I could quickly pick out poor hip extension, a lack of hip internal rotation, poor arm drive and so on, but one question still remained in the back of my mind.
Why does the person have a tight right psoas and why does their hip seem to want to avoid it’s natural internal rotation?
It is these questions to which a purely mechanical explanation is insufficient. Knowledge must be continually challenged and improved upon, so embrace the discomfort that comes with new information and prepare to see the walking brain in action.
Fixed Action Patterns (F.A.P’s) – playing to the same tune
Human locomotion is an interplay between neurological control and mechanical energy return mechanisms. Central Pattern Generators (C.P.G’s) are clusters of neurons that coordinate to facilitate fixed action patterns of muscle recruitment. If you think of the body as a band, the F.A.P of gait is like the drummer keeping time with the basic rhythm.
The reason we have C.P.G’s is to reduce the computational load of repetitive movements on the brain. Chewing, swallowing, breathing and walking all have hard wired circuits that hum away in the background allowing us to use our brain power for other things. The circuitry of gait produces an instantly recognisable and predictable pattern of motion among the entire race.
If we disregard instances of disease, injury and dysfunction for a moment, the individuality in human locomotion is in large part due to the uniqueness of the skeleton. Everyone has slightly different shaped femurs, pelvises, tibial varum, calcaneus’ etc. These variants will produces differences in locomotion from person to person but you should always see the classic counter rotation pattern of gait in every individual.
When this is missing, the drummer isn’t keeping time so there is most definitely something wrong.
Arm swing is initiated neurologically. It is not just a component of momentum and energy transferral through the kinetic chain. The motor and pre-motor cortex of the brains frontal lobes initiates arm swing. The right frontal cortex initiates the left shoulder to flex and swing the upper limb forward.
Team Hip and Shoulder
As I have described above the role of the Central Pattern Generator for gait is to fire the contralateral hip and shoulder simultaneously into flexion to produce counter rotation.
The ipsilateral hip and shoulder also have a distinct relationship, a relationship controlled by the Ponto-Medullary-Reticular-Formation (PMRF)
The PMRF or any reticular formation within the brain is a net like structure of cells that surround more formal structures and as such are privy to information from multiple systems. In this case the PMRF hangs around the Pons and Medulla Oblongata, two hugely important and influential parts of the brainstem.
The brainstem reticular formation resides within the brainstems core. It is made up of a number of cells of various size and shape, surrounded by a complex and structured network of overlapping fibres..
The PMRF has four main roles, the description of which somewhat outweigh the general tone of this article but of particular interest to trainers and therapists is its role in defined muscle facilitation.
The Ponto-Medullary-Reticular Formation facilitates extensor muscles above the level of T6 and flexor muscles below T6 Ipsilaterally. In gait this means that it drives the right shoulder into extension and the right hip into flexion. As well as facilitating these muscle groups, it should inhibit flexors above T6 and extensors/external rotators below. When you see a client with a dropped, internally rotated and flexed right shoulder and externally rotated right hip, the PMRF is not doing its job appropriately. The root cause of this extremely common postural deviation is a poorly functioning ipsilateral PMRF
Sweet, Sweet Ass
As the PMRF functions to facilitate the right hip into flexion and right shoulder into extension the cerebellum makes sure the left hip contracts appropriately into hip extension. One of the many roles of the cerebellum
a fascinating part of the brain which lies in between the brainstem and cortex, is to facilitate all extensor muscles ipsilaterally. A poorly functioning left cerebellum may result in weaker left extensors. If the glute, hamstring and erector spinae group are not being called into action by the cerebellum, we could see a wobbly head, internally rotated ipsilateral shoulder, tight ipsilateral quads and psoas and the subsequent poor hip extension.
Very impressive Mr Bond, but aren’t you forgetting something?
Absolutely. I have so far presented 1 spinal cord mechanism (C.P.G) and 3 cortical (brain based) mechanisms that control a most complex movement pattern that we all take for granted. If we’re going to continue this journey on the nerd express we’ll next look at the influence of the eyes and inner ear.
The visual system has dramatic influence over our movement and posture. So much so that it really warrants a series of articles all to itself. For the sake of this neurological explanation of gait let me explain that the visual system, vestibular system and spine are all intrinsically linked.
Not loosely linked but hard wired together via the Medial Longtitudinal Fasciculus. The M.L.F is a pair of ascending and descending cortical tracts that arise from the centre of the brainstem. They carry information from eye motion and head orientation via the vestibular system (inner ear) and coordinates recruitment of the intrinsic spinal muscles in response.
When I used to train MMA (cage fighting) they used to say ‘control the head and you control the fight’. Well the direction of the eyes controls the head and subsequently the spine. Essentially our gait is driven by the mechanisms described above and then directed via the eyes and ears.
While that seems fairly obvious there is a pretty cool mechanism at play that allows us to fix the eyes on a target while we are in motion. A mechanism that means our perception of the world doesn’t bounce and shake whenever we do. Ladies and Gentlemen please welcome, the Vestibular- Occular-Reflex (VOR)
Chickens are able to keep their heads stable even though their bodies are moving around. They do this because they don’t have the eye control needed to keep their eyes fixed on a stationary object while the rest of their body is moving. Therefore, they have automatic compensatory adjustments with the muscles in their head and neck instead. Contrastingly, humans have an eye movement handled by the vestibulo-ocular reflex (VOR) which keeps your vision stabilized when you move your head.
Without the Vestibular-Occular-Reflex whenever we move, run, walk, jump etc, the world would move too. The VOR allows us to maintain a fixed, steady gaze whilst in motion. It is the interplay between the vestibular and visual systems that means we can fixate our eye’s on an attractive young lady or man and not feel sick as we walk towards them because our eyes are held steady.
What about the spinal cord?
Each of the mechanisms described above may be quite new to you. They are cortical mechanisms that hum away in the background and make upright locomotion possible. Such an incredible system still wouldn’t be very successful if it wasn’t able to adapt to the challenges of the environment, so we now move on to the peripheral nervous system and the role of the muscle spindles.
Muscle spindles are part of the gamma motor system. They are a mechanism that reside in the belly of the muscle tissue in varying densities depending on the influence of the muscle. These guys are responsive to stretch. While the brain fires all of these wonderful mechanisms to allow us to walk, if we hit an uneven surface, slip, dodge, duck and weave through the urban jungle our muscle contractions have to adapt reflexively to keep us moving.
While the spindles do report into the brain, they need to respond instantly to perturbations and unpredictable interactions with the environment. As such they are able to adjust muscle recruitment extremely quickly via spinal cord circuitry.
All of this is carried out below our conscious awareness. In fact we may only become aware of our gait when we trip, step on something hard or sharp or for some reason direct our conscious awareness to it. Otherwise it’s just fairly effortless motion that gets us from A to B.
Get your wrench, its time for some mechanics
Worry not, the mechanics of the body does play a huge role in the efficiency of gait. Not in the initiation or control but definitely in ‘efficiency’.
We can’t very well have the muscles firing constantly every time we walk as it would be exhausting. Getting muscles to contract is energy consuming business. Instead we rely on a pretty popular connective tissue called fascia.
To ensure continual energy efficiency and endurance in locomotion we get to reap the benefit of some Neuro-mechanical Interplay. Efficient Gait requires oscillation between muscle and fascia.
This interplay maintains lumbar lordosis. As we move through the gait cycle the pelvis should have a balanced rotational quality to it. It moves through anterior, posterior and lateral tilts. If all of the muscles are working properly, this should translate into a nice even rotation in the transverse plane. When the pelvis posteriorises and the spine flexes, collagen – (the fascia) is loaded.
Collagen has elastic properties which make it a perfect energy return system. Stretch it a little and it will give you a kind of rebound contraction in return which reduces muscular effort.
The oscillation between contraction of the trunk and hip musculature and the energy return qualities of the thoraco-dorsal fascia generates an incredibly efficient mode of locomotion which is modulated by the central nervous system.
As I stated at the start of this article; human gait is a symphony of systems who’s basic rhythm is conducted by the brain. As an assess and reassess tool It offers the perfect platform.
Gait is autonomous and predictable. Therefore if we intervene as trainers and therapists with a particular exercise or stimulus and gait improves, its fair to say that we have done that individual some good.
At the end of the day, our job is to help people. To try and understand why they may not be moving well or are in pain. Pursuing an understanding of neurology even only to a superficial level will make you far better at what you do.
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